The present invention relates to a joint structure composed of flexible tubing and a handling apparatus constructed of such a joint structure for use in endoscopes. The joint structure composed of flexible tubing joins to another member. Specifically, the present invention relates to a joint structure consisting of one soft flexible tube and one hard flexible tube joined together by laser welding, and also to a flexible tube and a leading metal member joined together by laser welding.
As shown in FIG. 14, conventional forceps with endoscopes, are inserted through a forceps inlet (12) provided on an endoscope manipulator means (11). The forceps go through an insertion channel (not shown) stored within both a connection part (13) and a bendable part (14), and protrude from a forceps outlet (16) provided at the head (15) of the endoscope (10). At the leading edge, the forceps comprise, a pair of forceps cups (8) that are operated using a forceps manipulator means (21).
As shown in FIGS. 14 and 15, the forceps (17) comprises flexible tubing constructed of a coil-wound metal wire element that can be inserted through an insertion channel in the endoscope (10); and a flexible tubing support member (22) consisting of a forceps manipulator means (21), and a leading metal member (7) that has a pair of forceps cups (8) attached through an attachment pin (9) for opening and shutting the forceps cups (8), to the leading metal member (7). The support member (22), that is a part of the forceps manipulator means (21), connects through an excessive-bend preventor coil (20) to the base end (19) of the flexibble tube (18). The pair of forceps cups (8) connects to the leading end of an operation wire (25) through a pair of linking means (23) having a pair of back linking parts (24) protruding from the linking means (23), a pair of links (24') connected to the back linking parts (24), and a wire joint metal member (26). Numerals 27 and 28 are attachment pins for connecting the links (25). The base end of the operation wire (25) connects to an operation control (29) composing the forceps manipulating means (21).
When operating conventional forceps for endoscopes, the thumb is inserted into a hole bored in the flexible tubing support member (22), and the operation control (29) is held with the second and third fingers, so that relative movement between the operation control (29) and the support member (22) causes the forceps cups to open and shut.
When inserted in a body cavity, the bendable part (14) can be manipulated so that the leding end (15) can be pointed towards the body part that needs to be observed. The connector (13) is relatively elastic, and is flexible enough to facilitate insertion of the leading end (15) and the bendable part (14). The connector (13) also rotates together with the entire forceps manipulator means (11). Accordingly, the bendable part (14) can be bent at sharp angles, and the connector (13) is flexible with a somewhat low degree of curvature. The insertion channel stored within the two parts 14 and 13 has the same degrees of curvature at respective portions in accordance with the bending of the two parts 14 and 13.
In exactly the same way, the flexible tube (18) of the forceps for an endoscope (17) also has the same degrees of curvature ass the insertion channel. Accordingly, the flexible tubing (18) has: (a) a soft flexible tube (1) that bends in line with the bendable part (14); and (b) a hard, flexible, elastic tube (2) that follows the movement of the connector (13).
One way to form a flexible tube for use in a forceps device for an endoscope is to join and integrate the soft flexible tube (1) and the hard flexible tube (2). As shown in FIG. 16, each tube is made of metal wire elements, though the diameters and having an equal outside diameter. To join the two flexible tubes, the end face of each flexible tube is flattened, and the flexible tubings are butted face to face. The tubes are then welded together by irradiating a laser beam (31) onto the outer surface of the butted joint and forming a weld joint (3) on the whole of the outer surface, as shown in the section of the welded connection given in FIG. 17.
A conventional method for joining the flexible tube (1) and the leading metal member (7) is disclosed in Japanese Patent Publication No. 246741/1985. The method is schematically shown in FIG. 18. As shown in this figure and also in FIG. 19 (that depicts a section of the welded joint), either the soft flexible tube (1) or the leading metal member (7) is worked so that the flexible tubing (1) into the metal member (7). The tube and leading mumber are they welded together by irradiating a laser beam (31) onto the outer surface of the butted joint and forming a weld joint (3) on the whole of the outer surface. In this conventional method, the flexible tubing is made up of a metal wire element having a high corrosion resistance (e.g., stainless steel wire such as SUS 304-WPB for use in springs) wound in to a coil.
In the prior art, the austenitic stainless steel (represented by SUS 304) is not hardened by quenching. Work strain can be removed by decomposing chromium carbide by means of a solid-solution quenching from a high temperature (1010.degree.-1150.degree. C. in the case of SUS 304). Alternatively such austenitic steel can be hardened and its mechanical strength can be raised by strong cold working.
SUS 304-WPB is a metal wire element for use in the above-described flexible tubing and is manufactured by strongly cold-drawing a wire element of austenitic stainless steel SUS 304 after a solid solution treatment. Its hardness and mechanical strength are larger than those of SUS 304 wire heat-treated for solid solution but not cold-drawn.
In laser welding, the weld is heated above the melting point and the surrounding area is heated at a fairly high temperature. Accordingly, the weld and the surrounding area are annealed during welding and while cooling, and have significantly low mechanical strength--much lower than that of the SUS 304-WPB wire element.
Although the above description concerning the thermal effect during welding has been made with reference to austenitic stainless steel SUS 304, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation. Rather, the description is applicable to any materials mechanically strengthened by work-hardening. In general, metal wire elements for constructing flexible tubings (or coil springs) include various kinds of stainless steel wire, hard steel wire, piano wire, oil-tempered wire, and many others. Work-hardening raises the mechanical strength of most of these elements during cold-drawing, but heating lowers it during welding.
FIG. 20 shows an appearancce of the welded joint and surounding area, corresponding to the section of the welded joint of the soft flexible tube (1) to the hard flexible tube (2) shown in FIG. 17. FIG. 21 shows the welded joint and surrounding area correspondig to the welded joint of the soft flexible tube (1) to the leading metal member (7) shown in FIG. 19. In FIGS. 20 and 21, reference numerals 3 is the welded joint and 4 is the region thermally affected by laser welding. The range of the thermally affected region depends on the heat input by the laster beam, the diameter of the metal wire element composing the flexible tube (1), and other factors. In the above-described conventional laser welding, the thermally affected regions (4) have been annealed during the after welding, so their elastic limits are much lower than other portions of the flexible tube.
As shown in FIG. 22, when manipulating forceps for an endoscope, the welded joints (3) and their neighboring portions are bent or buckled to small radii by forces (32 and 33)--for example, when the user inserts the forceps forcefully through the forceps inlet in the face of resistance, or when the user handles the forceps with excessive force. In such cases, as shown in FIGS. 23 and 24, the thermally affected regions (4) are subject to plastic deformation or buckling and od not recover their original shape. In the particular case of a joint structure comprising a soft flexible tubing (1) and a hard flexible tubing (2), as shown in FIG. 23, both the wire element diameter and elastic limit of the soft flexible tube are lower than those of the hard flexible tube, and hence plastic deformation or buckling occurs more often in the thermally affected region of the soft flexible tube.